The hadori is a thin, braided leather cord, that Malkieri men wore around their foreheads to hold their hair back (NS, Ch. 1), in pledge that they will fight the Shadow (KoD, Ch. 20). Many Malkieri have abandoned it, but some keep to it, either in respect for their traditions, or to make others nervous (KoD, Ch. 20). Those that do wear it are buried wearing just the hadori (NS, Ch. 1). As with the other borderland nations, a boy is considered a man when given a sword, but in Malkier, the hadori was considered more important (TSR, Ch. 16).
"Once that was tied around his head, he alone decided where he went, and when, and why" (Lan, The Shadow Rising, Chapter 16)